With the rapid development of the light source of light-emitted diode (LED) and solar energy, the enhancement smaller size of optoelectronic products have been provoked. Plastics materials have been widely used in precise molding optical components the optoelectronic products, especially for the mobile devices. Further, optical lens used in the optoelectronic products gradually downsizes so the hybrid optical elements (HOEs) have been developed to be one solution to replace the complicated optical lens set.
For molding optical components with optical plastic, include injection molding and hot embossing have been considered and applied in current development and production. Since the smaller feature and shorter life cycle of related consumer electronics product has been a tendency in market, the plastics materials gradually replace the optical glass. Advantages of plastics materials include the lower weight and density, easily formed the complicated curved surface, mass production, low cost and no secondary processing. When the mobile phone with picture-taking function of high display quality and micro-projector have been developed, it is necessary to shrink the size of the optical component and also with structured optics for better optical image quality.
Basically, the factors associated with the optical plastic component of HOE or aspherical lens with micro structures include: (1) form error; (2) groove filling rate; and (3) residual stress. The form error is obtained after molding material injected into mold cavity, which results in the optical design deviation of the plastic component due to the materials shrinkage of molding part, and the optical image quality is downgraded. The groove filling rate is easily limited to the manufacturing process and multi-scale dimension consideration, which causes the design size and shape of the microstructure to be deviated after a molding step and debit effects on the optical property. When the optical plastic components are injected, the plastic subjected to the steps of high temperature, high pressure and high shear stress so that the residual stress, is induced in the molding part. The residual stress during the injection molding step includes: the flow-induced cause; and (2) the thermally induced cause. Besides the stress birefringence induced by the residual stress affects the optical property of the molding part, a crack, shrinkage and warped appearance and lower mechanical strength may be simultaneously induced.
The various factors during the process of injection molding will affect the form error, the groove filling rate and residual stress in different levels and thus the three properties should be evaluated correctly. Consequently, there is a need to develop a novel molding device and molding method to solve the aforementioned problems of form error, groove filling rate of microstructure and residual stress for the effect on the optical quality, especially for HOE of optical applications.